There are more than a million Americans who are infected with HIV. Highly effective antiretroviral therapy (ART) makes it possible for persons living with HIV (PLWH) to have longer, healthier lives. Despite treatment advances, only a quarter of PLWH successfully keep the virus under control. Medication non-adherence is a significant contributor to unsuccessful viral suppression. As a result, interventions targeting adherence have been developed, with most interventions demonstrating some degree of success in the short-term. However, the impact of these interventions is generally not sustained over time, and it is not feasible to deliver more intensive adherence interventions in most HIV treatment settings. As a result, there has been interest in developing efficacious electronically-delivered interventions. This work is still in its infancy, and there is a paucity of work that has been done to establish the efficacy of mobile health ART adherence applications. A mobile health application would maximize the portability of the intervention and allow for real-time adherence tracking and feedback and ready access to content or services to enhance adherence. The present proposal aims to develop and refine a mobile health ART adherence application and to conduct a preliminary randomized controlled trial (RCT) comparing a face-to-face ART adherence intervention followed by the mobile health ART adherence application (mARTAA) to the face-to-face adherence intervention alone, which approximates standard-of-care (SOC). The long-term goal of this line of research is to disseminate an efficacious, mobile health ART adherence application that can be integrated readily into clinical care. In Phase 1 of the proposed study, we will develop and refine mARTAA using an iterative process of piloting and modification based on data collected from pilot participants (n=20). Phase 2 (n=60) will consist of a preliminary RCT comparing mARTAA and SOC. Participants in the RCT will complete a baseline interview and follow-up interviews at 1, 3, 6, and 12 months. The primary outcome variable will be ART adherence based on electronic pill box data. We expect that, as a result of this project, we will have developed and demonstrated the efficacy of a mobile health application to improve ART adherence that can be disseminated easily into real-world clinical settings. Such an intervention holds the promise of improving HIV viral suppression, slowing disease progression, reducing HIV-related morbidity and mortality, decreasing the risk of HIV infection in others, and minimizing the production of treatment resistant strains of HIV.